JP2018090900A - Iron-base sintered alloy valve seat for internal combustion engines with excellent wear resistance and a combination of valve seat and valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a valve seat made of an iron-based sintered alloy for an internal combustion engine having excellent wear resistance and a combination of a valve seat and a valve having excellent wear resistance. SOLUTION: The matrix phase is a fine carbide precipitation phase in which fine carbides of 10 μm or less are precipitated and the hardness is 550 HV or more in Vickers hardness, and the hardness of 650 to 1200 HV in Vickers hardness is set in the matrix phase. Iron having a structure in which hard particles having an area ratio of 20 to 40% are dispersed, a diffusion phase is formed in an area ratio of more than 0% and 5% or less, and solid lubricant particles are dispersed in an area ratio of 0 to 5%. The valve seat is made of a base sintered alloy. As a result, even if a valve with a high face hardness of 400 HV or more and even 600 HV or more is used, the wear of the opposing valve seats is small, and a combination of a valve and a valve seat with excellent wear resistance can be realized. The durability of the valve mechanism is significantly improved. [Selection diagram] None

Description

  The present invention relates to a valve seat for an internal combustion engine, and more particularly to an improvement in wear resistance of a valve seat for an internal combustion engine that uses a gas fuel such as LPG or CNG and a special fuel containing ethanol.

  The valve seat is press-fitted or joined to the cylinder head of the internal combustion engine, and serves to cool the combustion gas seal and the valve. The valve seat is hit by a valve, and is exposed to wear due to sliding, heating by combustion gas, corrosion by combustion products, and the like, so that it has been conventionally required to have excellent heat resistance and wear resistance. Recently, from the viewpoint of the preservation of the global environment, there are increasing demands for internal combustion engines for automobiles in addition to higher performance, fuel efficiency improvement, exhaust gas purification, and the like. In order to cope with such demands, the operating conditions of the internal combustion engine for automobiles are set to severe conditions, the combustion conditions become severe, and the usage environment of the valve seats used is further severe. Therefore, the conventional valve seat has a problem that the characteristics such as heat resistance and wear resistance are insufficient.

  For such a problem, for example, Patent Document 1 describes “a valve seat for an internal combustion engine made of wear-resistant sintered alloy”. In the technique described in Patent Document 1, fine carbides of 10 μm or less are precipitated, the hardness is 400 HV or more, the first phase mainly composed of Fe is 30 to 95% in area ratio, and Fe is the major component. And a valve seat for an internal combustion engine having excellent wear resistance, the main structure of which is an iron-based matrix structure composed of a mixed structure in which the second phase is softer than the first phase and the area ratio is 5 to 70%. In the technique described in Patent Document 1, the wear resistance is improved by allowing the first phase having a high hardness to exist in an area ratio of 30% or more. Further, the valve seat described in Patent Document 1 is said to be suitable as a valve seat for an internal combustion engine under severe operating conditions.

  Further, in Patent Document 2, it is defined by other impurities of 8 to 12% by weight of chromium, 0.5 to 3% by weight of molybdenum, 1.5% by weight or less of vanadium, 0.2 to 1.5% by weight of carbon, and 2% by weight maximum, and iron as the balance. An iron-based sintered material characterized in that it has a porous martensite matrix of the composition described below, which matrix has supermicroscopic particles of molybdenum rich carbides, which are virtually uniformly dispersed. Have been described.

JP-A-10-226855 Japanese Patent Laid-Open No. 05-5163

  In recent years, internal combustion engines have come to be used in a wide variety of fuels such as gasoline and heavy oil, as well as special fuels such as gas and ethanol. It is speculated that if the fuel to be used is different, the combustion conditions such as the combustion temperature and the generated combustion gas will be different, and the use environment of the internal combustion engine will be different. For example, when the fuel used is gas fuel, the usage environment such as a valve seat becomes more severe. This is because gas fuel is less likely to produce combustion products than gasoline and light oil, and is in an environment where wear due to metal surface contact is likely to proceed.

  Further, conventionally, a nitride film formed on the surface for improving the slidability of the valve has been removed by polishing or the like in the vicinity of the contact surface with the valve seat. However, due to recent demands for cost reduction, polishing or the like is not performed even in the vicinity of the contact surface with the valve seat in order to remove the nitride film or the like. In many cases, the nitride film or the like formed on the surface of the valve is used as it is, even though it is in the vicinity of the contact surface with the valve seat, thinly remaining on the contact surface with the valve seat. The nitride film formed on the surface is hard at 1000 HV or more, and when such a valve is used, even a valve seat manufactured by the technique described in Patent Document 1 or Patent Document 2 is worn. In particular, there has been a problem that it becomes prominent in a use environment where metal contact is likely to occur, such as when using a special fuel such as a gas fuel.

The present invention solves such a problem, and can be used for an internal combustion engine having excellent wear resistance that can maintain excellent wear resistance even in a use environment in which metal contact is likely to occur using special fuel such as gas fuel. An object of the present invention is to provide a ferrous sintered alloy valve seat and a combination of a valve seat and a valve excellent in wear resistance. In addition, from the viewpoint of workability and drop-off resistance, the valve seat targeted by the present invention has a crushing strength of 45 kgf / mm ² (441 MPa) or more obtained in accordance with the provisions of JIS Z 2507.

  In order to achieve the above-mentioned object, the present inventors diligently studied various factors that affect the wear resistance of a valve seat when a valve seat and a valve having a surface hardness that is “harder” than before are combined. . As a result, in a combination of such a “hard” valve and a conventional valve seat as described in, for example, Patent Document 1, adhesion occurs in the valve seat and a special fuel such as gas fuel is used. It has been found that there is a problem that the wear resistance is remarkably lowered particularly in the use environment where metal contact is likely to occur. The present inventors have found that such a decrease in wear resistance is that the structure of the valve seat contains a soft phase, and in order to prevent such a decrease in wear resistance, It has been thought that it is effective to reduce the difference in hardness between the surface, the matrix phase and the hard particles. That is, it has been found that it is effective to reduce the soft phase and to make the base phase a structure composed of a substantially uniform hard phase of 550 HV or higher in order to prevent a decrease in wear resistance of the valve seat.

  Further, the present inventors have found that the base phase is a fine carbide precipitation phase in which fine carbides having a particle size of 10 μm or less are precipitated and have a Vickers hardness of 550 HV or more, and a Vickers hardness of 650 HV or more. It has been found that a valve seat having a structure in which hard particles having a particle are dispersed in the matrix phase provides a valve seat with excellent wear resistance and crushing strength.

  The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.

  (1) A valve seat made of an iron-based sintered alloy in which hard particles and solid lubricant particles are dispersed in a matrix phase, wherein the matrix phase precipitates fine carbides having a particle size of 10 μm or less, and Vickers hardness In the fine carbide precipitation phase having a hardness of 550 HV or more, the hard particles have a Vickers hardness of 650-1200 HV, the hard particles in the matrix phase in an area ratio of 20-40 And a structure in which a diffusion phase is formed around the hard particles in an area ratio of more than 0% and 5% or less, and the solid lubricant particles are dispersed in an area ratio of 0 to 5%. Valve seat made of iron-based sintered alloy with excellent wear resistance for internal combustion engines.

  (2) In (1), the base part containing the base phase, the diffusion phase, the hard particles and the solid lubricant particles is in mass%, C: 0.5 to 2.0%, Si: 0.5 to 2.0%, Mn : 5% or less, Cr: 2 to 15%, Mo: 5 to 20%, Co: 2 to 30%, V: 0 to 5%, W: 0 to 10%, Ni: 0 to 5% , S: 0 to 2%, Cu: 0 to 5%, Ca: 0 to 5%, F: 0 to 5%, including one or more selected from the balance Fe and inevitable impurities A valve seat made of an iron-based sintered alloy for an internal combustion engine, characterized by having the composition

  (3) In (1) or (2), the hard particles contain, in mass%, Cr: 3 to 15%, Mo: 20 to 40%, Si: 0 to 3%, Fe: 0 to 3 Mo—Cr—Co intermetallic compound particles comprising Co and the inevitable impurities, Mo: 20-30%, Ni: 5-20%, Cr: 15-35%, and Si: Mo-Cr-Ni-Co-based intermetallic compound particles containing 0 to 3%, remaining Co and inevitable impurities, Mo: 20 to 40%, Cr: 3 to 15%, Si: 0 to Mo-Cr-Fe-based intermetallic compound particles containing 3% balance Fe and inevitable impurities, and Mo: 30-50%, Fe: 15% or less, further Cr: 2-8%, Si : One or more selected from Mo-Fe-Co intermetallic compound particles containing 0 to 4%, the balance being Co and inevitable impurities, iron for internal combustion engines, Base sintered alloy valve seat.

(4) In (2) or (3), the solid lubricant particles are one or more selected from manganese sulfide MnS, molybdenum disulfide MoS ₂ , and calcium fluoride CaF _2. An iron-based sintered alloy valve seat for an internal combustion engine.

  (5) A combination body of a valve and a valve seat, wherein the valve has a contact surface with the valve seat having a surface hardness of 400 to 1300 HV in terms of Vickers hardness. A valve / valve seat combination with excellent wear resistance, characterized in that the valve seat is made of an iron-based sintered alloy for an internal combustion engine according to any one of (4) to (4).

  According to the present invention, in an internal combustion engine that uses a special fuel such as gas fuel, which is a severe wear environment, the face face is hard as a valve, even if a high face face hardness valve is used, There is little wear of the valve seats facing each other, and it is possible to realize a combination of a valve and a valve seat having excellent wear resistance, and it has a remarkable industrial effect. Further, according to the present invention, there is an effect that the durability of the valve mechanism is remarkably improved.

It is explanatory drawing which shows the outline | summary of a rig testing machine.

  The iron-based sintered alloy valve seat of the present invention is a valve seat having a structure in which hard particles or further solid lubricant particles are dispersed in a matrix phase. The base phase is a phase having a Vickers hardness of 550 HV or higher.

  If the hardness of the base phase is less than 550 HV, adhesion is likely to occur due to contact with a valve, particularly with a valve having a high surface hardness, and the desired wear resistance cannot be ensured. On the other hand, when the hardness exceeds 700 HV, the toughness as a sintered body decreases. For this reason, the hardness of the matrix phase is limited to a range of 550 HV or more, preferably 700 HV or less in terms of Vickers hardness. In addition, Preferably it is 600-650HV.

  The matrix phase having such a hardness has a hard single-phase structure that is a fine carbide precipitation phase in which fine carbides of 10 μm or less are precipitated. The term “single phase” as used herein refers to a case where the phase occupies 95% or more by area ratio. If the area ratio is less than 5%, even if a phase having a hardness of less than 550 HV remains in the matrix phase, the influence on the wear resistance is small and acceptable.

  If the particle size of the carbide precipitated in the matrix phase exceeds 10 μm, the hardness and toughness of the matrix phase will decrease, the opponent attack will increase, and the crushing strength will decrease. For this reason, the matrix phase having a hardness of 550 HV or more is preferably a fine carbide precipitation phase in which fine carbides of 10 μm or less are precipitated.

  The matrix phase having the above hardness and structure is in mass%, C: 0.5 to 2.0%, Si: 0 to 1.0%, Mn: 0.05 to 5%, Cr: 0 to 5.0%, Mo: 0 to 8.0%, V: 0 to 5.0%, W: 0 to 10.0%, Co: 0 to 5.0%, preferably having a composition composed of the remaining Fe and inevitable impurities.

  The valve seat of the present invention has a structure in which hard particles or further solid lubricant particles are dispersed in a matrix phase having the above-described hardness, composition, and structure. The hard particles to be dispersed are hard particles having a Vickers hardness of 650 to 1200 HV. When the hardness of the hard particles is less than 650 HV, the effect of improving the wear resistance is small. On the other hand, when the hardness exceeds 1200 HV, the machinability is reduced. For this reason, the hardness of the hard particles dispersed in the matrix phase is limited to the range of 650 to 1200 HV in terms of Vickers hardness.

  In the present invention, the hard particles dispersed in the matrix phase preferably have the above hardness and have an average particle size of 10 to 150 μm. If the average particle size is less than 10 μm, it tends to diffuse during sintering, and a desired improvement in wear resistance cannot be ensured. On the other hand, if it exceeds 150 μm, the bond strength with the base decreases. For this reason, it is preferable to limit the average particle diameter of the hard particles dispersed in the matrix phase to a range of 10 to 150 μm. Here, the “average particle diameter” means a particle diameter D50 at which the cumulative distribution measured by the laser scattering method is 50%.

  In the valve seat of the present invention, the hard particles having the above hardness are dispersed in an area ratio of 20 to 40% in the matrix phase. If the dispersion amount of the hard particles is less than 20%, desired wear resistance in a severe environment cannot be secured. On the other hand, if it exceeds 40%, the bonding strength between the matrix phase and the hard particles is lowered, and the wear resistance is lowered.

  The hard particles used in the valve seat of the present invention include Mo-Cr-Co intermetallic compound particles, Mo-Cr-Ni-Co intermetallic compound particles, Mo-Cr-Fe intermetallic compound particles, Mo-Fe It is preferable to use one or more selected from —Co based intermetallic compound particles.

  Mo-Cr-Co-based intermetallic compound particles contain, by mass%, Cr: 3 to 15%, Mo: 20 to 40%, Si: 0 to 3%, Fe: 0 to 3%, It has a composition consisting of the balance Co and inevitable impurities, and after sintering, the hardness is 650-850 HV. The Mo-Cr-Ni-Co intermetallic compound particles include Mo: 20 to 30%, Ni: 5 to 20%, Cr: 15 to 35%, and further Si: 0 to 3%. It has a composition consisting of the balance Co and inevitable impurities, and has a hardness of 900 to 1200 HV. The Mo—Cr—Fe intermetallic compound particles contain Mo: 20 to 40%, Cr: 3 to 15%, further contain Si: 0 to 3%, and the balance is Fe and inevitable impurities. And the hardness is 750 to 1050HV. Further, the Mo-Fe-Co intermetallic compound particles contain Mo: 30 to 50%, Fe: 15% or less, further contain Cr: 2 to 8%, Si: 0 to 4%, and the balance Co and It has a composition consisting of inevitable impurities and has a hardness of 900 to 1200 HV.

  The valve seat of the present invention has a structure in which a diffusion phase is generated around hard particles. This diffusion phase is formed by diffusing the alloy element from the hard particles into the matrix phase during sintering, and has an action of preventing the hard particles from falling off the matrix phase. For this reason, even if hard particles are dispersed in a large amount, it is considered that the hard particles can be prevented from falling off from the matrix phase, and the reduction of the crushing strength can be suppressed by the presence of the diffusion phase.

  In order to obtain such an effect, it is preferable that the diffusion phase has an area ratio of 0% to 5% or less. When the diffusion phase exceeds 5%, the hardness decreases and the desired wear resistance cannot be ensured. The formation of the diffusion phase depends on the sintering temperature and sintering time, and the sintering temperature and time are adjusted so that the abundance (area ratio is 5% or less) described above. It is preferable.

In the valve seat of the present invention, solid lubricant particles may be further dispersed in an area ratio of 0 to 5% in the matrix phase. Dispersion of solid lubricant particles in the matrix phase improves machinability, workability, and lubricity. However, if it exceeds 5%, the progress of the sintering reaction is hindered and the mechanical properties are deteriorated. For this reason, it is preferable to limit the solid lubricant particles to an area ratio of 0 to 5%. Examples of the solid lubricant include manganese sulfide MnS, molybdenum disulfide MoS ₂ , calcium fluoride CaF ₂ , and the like.

  Thus, in the valve seat of the present invention, the hard particles having the above-described hardness and the solid lubricant particles having the above-described composition are dispersed in a predetermined amount in the matrix phase having the above-described structure and hardness. Has a structure in which a diffusion phase is formed.

  The base portion including the base phase, hard particles, and solid lubricant particles is in mass%, C: 0.5 to 2.0%, Si: 0.5 to 2.0%, Mn: 5% or less, Cr: 2 to 15%, Mo: 5 -20%, Co: 2-30%, V: 0-5%, W: 0-10%, Ni: 0-5%, S: 0-2%, Cu: 0-5%, It contains one or more selected from Ca: 0 to 5% and F: 0 to 5%, and has a composition consisting of the balance Fe and inevitable impurities.

  Hereinafter, the reason for limitation in the base portion composition will be described. Hereinafter, the mass% in the composition is simply expressed as%.

C: 0.5-2.0%
C is an element necessary for adjusting the matrix phase to a predetermined hardness and structure, or for forming carbides, and is contained in an amount of 0.5% or more. On the other hand, if the content exceeds 2.0%, the melting point is lowered and liquid phase sintering is performed. When liquid phase sintering is used, the amount of precipitated carbide becomes excessive, the number of pores increases, the elongation characteristics deteriorate, and the dimensional accuracy decreases. For this reason, it is preferable to limit C to 0.5 to 2.0% of range. In addition, More preferably, it is 0.5 to 1.75%.

Si: 0.5-2.0%
Si is an element mainly contained in hard particles to form silicide and increase hardness, and is preferably contained in an amount of 0.5% or more. On the other hand, if the content exceeds 2.0%, the toughness decreases. For this reason, it is preferable to limit Si to 0.5 to 2.0% of range. More preferably, it is 0.5 to 1.5%.

Mn: 5% or less
Mn is an element that increases the hardness of the matrix phase, and Mn is an element that is included in the matrix due to the inclusion of solid lubricant particles and contributes to the improvement of machinability, containing 0.05% or more It is preferable to do. On the other hand, if the content exceeds 5%, the matrix phase hardness, toughness, and ductility are reduced with the stabilization of the structure, so Mn is preferably limited to 5% or less. More preferably, it is 0.05 to 3.5%.

Cr: 2-15%
Cr is an element that dissolves in the matrix phase and forms carbides to increase the hardness of the matrix phase, further increase the hardness of the hard particles, and improve heat resistance and wear resistance. It is preferable to contain 2% or more. On the other hand, if the content exceeds 15%, Cr carbide precipitates excessively, making it difficult to obtain fine carbide. For this reason, Cr is preferably limited to a range of 2 to 15%. In addition, More preferably, it is 2.5 to 12.5%.

Mo: 5-20%
Mo is an element that dissolves in the matrix phase and precipitates as a carbide, increases the hardness of the matrix phase, further contributes to an increase in hardness of the hard particles, and improves wear resistance. It is preferable to contain 5% or more. If it is less than 5%, the amount of precipitates is insufficient, and the desired wear resistance cannot be ensured. On the other hand, when it contains exceeding 20%, a moldability will fall. For this reason, Mo was limited to the range of 5 to 20%. In addition, More preferably, it is 7.5 to 17.5%.

Co: 2-30%
Co is an element that increases the strength of the matrix phase, particularly the high-temperature strength, contributes to the improvement of wear resistance, further improves the toughness of the matrix phase, and further contributes to the increase in hardness of the hard particles, Contain 2% or more. On the other hand, if it contains more than 30%, the base phase hardness is lowered and the desired properties cannot be secured. For this reason, Co was limited to a range of 2 to 30%.

  The above-mentioned components are basic components. In addition to the basic components, V: 0-5%, W: 0-10%, Ni: 0-5%, S: 0-2%, One or more selected from Cu: 0 to 5%, Ca: 0 to 5%, and F: 0 to 5% can be included.

V: 0-5%
V is an element that precipitates as a carbide, increases the hardness of the matrix phase, and improves the wear resistance, and can be contained as necessary. When it contains, it is preferable to contain 0.5% or more. If it is less than 0.5%, the amount of precipitates is insufficient, and the desired wear resistance cannot be ensured. On the other hand, when it contains exceeding 5%, moldability will fall. For this reason, V was limited to the range of 0 to 5%. In addition, More preferably, it is 0.5 to 2.5%.

W: 0-10%
W is an element that precipitates as fine carbides, increases the hardness of the matrix phase, and improves the wear resistance, and can be contained as necessary. When it contains, it is preferable to set it as 0.5% or more. If it is less than 0.5%, the amount of precipitates is insufficient, and the desired wear resistance cannot be ensured. On the other hand, when it contains exceeding 10%, a moldability will fall. For this reason, W was limited to the range of 0 to 10%. In addition, when it contains, More preferably, it is 0.5 to 7.5%.

Ni: 0-5%
Ni is an element that contributes to improving the strength and toughness of the matrix phase, and is an element that contributes to an increase in the hardness of the hard particles, and can be contained as necessary. When it contains, it is preferable to set it as 2% or more. On the other hand, if it exceeds 5%, the moldability of the matrix phase is lowered. For this reason, Ni is preferably limited to a range of 0 to 5%. In addition, when it contains, it is 2 to 4% more preferably.

S: 0-2%
S is an element that is contained in the base portion due to the inclusion of the solid lubricant particles and contributes to the improvement of the machinability, and can be contained as necessary. When S exceeds 2%, toughness and ductility are reduced. For this reason, when it contains, it is preferable to limit S to 2% or less.

Cu: 0 to 5%
Cu is an element that contributes to improving the strength and toughness of the matrix phase, and can be contained as necessary. If Cu is contained in excess of 5%, it leads to a decrease in adhesion. For this reason, when it contains, it is preferable to limit to 5% or less.

Ca: 0 to 5%
Ca is an element that is contained in the base portion due to the inclusion of solid lubricant particles and contributes to improvement of machinability, and can be contained as necessary. When Ca is contained in excess of 5%, ductility is reduced. For this reason, when it contains, it is preferable to limit to 5% or less.

F: 0-5%
F is an element that is contained in the base portion due to the inclusion of the solid lubricant particles and contributes to the improvement of the machinability, and can be contained as necessary. When F exceeds 5%, ductility is reduced. For this reason, when it contains, it is preferable to limit to 5% or less.

  The balance other than the above components is Fe and inevitable impurities. As an inevitable impurity, P: 0.1% or less is acceptable.

Below, the preferable manufacturing method of this invention valve seat is demonstrated.
First, the iron-base powder forming the matrix phase, the alloy element powder, the hard particle powder, and the solid lubricant particle powder are blended, mixed, and kneaded so as to have the predetermined valve seat composition described above. Use mixed powder. In addition, it is preferable that the iron-base powder mix | blended with mixed powder shall be alloy steel powder which has a composition close | similar to the above-mentioned base phase composition from a uniform viewpoint.

  The alloy steel powder is preferably a high-speed tool steel composition powder defined in JIS G 4403. The high-speed tool steel is preferably made of Mo. In addition to the high-speed tool steel composition described above, the alloy steel powder has a composition that has a hardness of 550 HV or higher and can become a fine carbide precipitation phase as the base phase of the valve seat of the present invention. There is no problem using alloy steel. Needless to say, in the mixed powder, in addition to the alloy steel powder described above, graphite powder and further alloy element powder are blended so as to have the matrix phase composition described above. In addition, you may mix | blend lubricants, such as a zinc stearate, with mixed powder.

  Next, the obtained mixed powder is filled into a mold and pressed by a press machine to obtain a green compact of a valve seat shape having a predetermined size and shape. The green compact is then subjected to a sintering treatment to obtain a sintered body.

In the present invention, the sintering treatment is preferably performed in a protective atmosphere at a temperature range of 1100 to 1200 ° C. for a holding time of 6 hours or more. When the heating temperature is less than 1100 ° C., the sintering diffusion is insufficient, and when it exceeds 1200 ° C., hard particles and matrix are excessively diffused, and the wear resistance is lowered. Needless to say, the press-sintering step may be repeated a plurality of times.
The obtained sintered body is processed into a valve seat (product) having a desired dimension and shape by processing such as grinding and cutting.

  The valve seat of the present invention is preferably used in combination with a valve having a surface hardness of the contact surface (valve face surface) with the valve seat of 400 HV or more, preferably 600 to 1300 HV. Valves having the above-mentioned surface hardness include valves having a nitride film formed on the surface using a heat-resistant steel as a base material (austenitic heat-resistant steel valves with a nitride film), and nitride films on the surface using a non-ferrous alloy as a base material. Valve made of special alloy with nitride coating, valve with nitride film formed on the surface of special alloy steel (special alloy steel valve with nitride coating), and trivalloy alloy Examples include a primed valve (trivalloy-type alloy primed valve), a stellite-type alloy, and a graded-valve primed with an iron-based alloy (stellite-type alloy primed valve, iron-based alloy primed valve). The valve seat of the present invention is used in combination with a valve having a surface hardness of 400 HV or higher, preferably 600 HV or higher when used in combination with a valve having a surface hardness of the valve seat of less than 400 HV. The amount of wear of the valve and valve seat is increased as compared with the case of using the above, and a desired improvement in wear resistance cannot be expected. The valve seat of the present invention can be expected to improve the desired wear resistance only when combined with a hard valve having a surface hardness of the contact surface (valve face surface) with the valve seat of 400 HV or higher, preferably 600 HV or higher.

  Hereinafter, based on an Example, this invention is demonstrated further.

Example 1
An iron-based powder for forming a base phase, a hard particle powder, an alloy element powder, and a solid lubricant powder are adjusted so as to have the blending amounts shown in Table 1, mixed, kneaded, and mixed powder did. The iron-based powder used was a powder having the composition shown in Table 2, and the used hard particle powder and solid lubricant particle powder were particle powders shown in Table 3. In some cases, mixed powder in which pure iron powder was mixed with iron-based powder was used. The mixed powder was mixed with 1 part by mass of zinc stearate as a lubricant with respect to 100 parts by mass of the mixed powder.

The resulting mixed powder is then filled into a mold and pressed into a green compact with a specified valve seat shape using a press machine, and further subjected to sintering at 1150 ° C for 360 minutes in a protective atmosphere. The body.
The obtained sintered body was further subjected to processing such as cutting and polishing to obtain a ferrous sintered alloy valve seat having a predetermined dimensional shape (outer diameter: 27 mmφ × inner diameter: 22 mmφ × thickness: 6 mm).

The obtained valve seat was subjected to structure observation, hardness test, wear test, and crushing strength test. The test method is as follows.
(1) Microstructure observation About the obtained valve seat, the cross section perpendicular to the axial direction is polished, corroded (corrosive liquid: nital liquid), the structure is revealed, and observed with an optical microscope (magnification: 200 times). The type of phase organization was identified. In addition, using a scanning electron microscope (magnification: 2000 times), the particle size of the carbide precipitated in the matrix phase was measured, and it was confirmed that the maximum particle size of the carbide was 10 μm or less. It was assumed that it was a fine carbide precipitation phase. When the maximum diameter of the carbide particle size (long side length) exceeded 10 μm, the carbide precipitation phase was simply used.
(2) Hardness test For the obtained valve seat, the cross section is polished, corroded (corrosive solution: nital solution) to reveal the structure, and then used as a base with a Vickers hardness tester (test force: 0.98 N (100 gf)) The Vickers hardness HV of the phase was measured. In addition, when the base phase was two phases, it measured separately about each phase.
(3) Wear test About the obtained valve seat, the wear test was implemented on the test conditions shown below using the rig testing machine shown in FIG.
Test temperature: 300 ° C (sheet face)
Test time: 12hr
Cam rotation speed: 3000rpm
Valve speed: 20rpm
Impact load: 700N
Valve material: Heat-resistant steel with nitride film (Steel type: SUH35 surface hardness 1150HV)
After the test, the amount of wear of the test piece (valve seat) was measured. From the obtained amount of wear, the valve seat No. 1 was used as a reference (1.00), and the wear ratio of the valve seat was calculated.
(4) Crush strength test The crush strength (kgf / mm ² ) of the obtained valve seat was determined in accordance with JIS Z 2507.

  Table 4 shows the obtained results.

Each of the inventive examples is a valve seat having a lower wear ratio and superior wear resistance than the conventional example (valve seat No. 1A), and having a crushing strength almost equal to that of the conventional example. On the other hand, in the comparative example out of the scope of the present invention, the crushing strength is equal to or higher than that of the conventional example, but the wear ratio is high.
(Example 2)
For the valve seats No. 1A, No. 3A, No. 4A, and No. 11A produced in Example 1, a wear test was performed by changing the valve material. Valve materials include No.1 nitride-coated austenitic heat-resistant steel (surface hardness 1150HV), No.2 nitride-coated special alloy steel (surface hardness 950HV), No.3 nitride-coated martensitic heat-resistant steel ( Surface hardness 850HV), No.4 Trivalloy alloy plating (surface hardness 780HV), No.5 Stellite alloy plating with nitride coating (surface hardness 700HV), No.6 Stellite alloy plating (surface hardness) 425 HV), No. 7 iron-based alloy plating (surface hardness 415 HV), and No. 8 special alloy steel (surface hardness 380 HV). Test conditions other than the valve material were the same as in Example 1.

  The evaluation of wear resistance is based on the combination of valve seat No.1A (conventional example) and valve No.2 (special alloy steel valve with nitride coating) as standard (1.00). The ratio of wear amount (wear ratio) when combined with a valve was determined and performed.

  The results obtained are shown in Table 5.

本発明例（バルブシートNo.3A）は、表面硬さ(バルブフェース面硬さ)が400HV以上の硬いバルブと組み合わされても、摩耗比は基準（1.00）より低くなっており、従来例に比べて、耐摩耗性が向上している。とくに、本発明例は、バルブの表面硬さが600HV以上である場合に、従来例（バルブシートNo.1A）に比べて耐摩耗性の向上が顕著となっている。なお、本発明例（バルブシートNo.3A）は、表面硬さ(バルブフェース面硬さ)が400HV以上である「硬い」バルブ（バルブNo.1〜No.7）と組み合わせた場合、組み合わせたバルブによらず、従来例（バルブシートNo.1A）に比べて、摩耗比は低くなっており、従来例に比べて耐摩耗性が向上している。なお、本発明例は、表面硬さが400HV未満のバルブ（No.8）と組み合わせた場合には、従来例と同等の摩耗比となり、耐摩耗性の向上は認められない。

In the present invention example (valve seat No. 3A), the wear ratio is lower than the standard (1.00) even when combined with a hard valve with a surface hardness (valve face surface hardness) of 400HV or higher. Compared to wear resistance. In particular, in the example of the present invention, when the surface hardness of the valve is 600 HV or more, the improvement in wear resistance is remarkable as compared with the conventional example (valve seat No. 1A). In addition, the present invention example (valve seat No. 3A) was combined when combined with a “hard” valve (valve No. 1 to No. 7) having a surface hardness (valve face surface hardness) of 400 HV or more. Regardless of the valve, the wear ratio is lower than the conventional example (valve seat No. 1A), and the wear resistance is improved compared to the conventional example. In addition, when the example of the present invention is combined with a valve having a surface hardness of less than 400 HV (No. 8), the wear ratio is the same as that of the conventional example, and no improvement in wear resistance is observed.

  On the other hand, any of the comparative examples outside the scope of the present invention has a higher wear ratio and lower wear resistance than the conventional example (valve seat No. 1A), regardless of the combined valve. In particular, when combined with a “hard” valve (valve No. 1 to No. 5) having a surface hardness (valve face hardness) of 600 HV or more, the wear resistance is significantly reduced.

  Thus, it can be seen that the valve seat of the present invention has the effect of significantly improving wear resistance when combined with a valve having a surface hardness of 400 HV or higher, particularly 600 HV or higher.

1 Valve seat 2 Cylinder block equivalent material 3 Heating means 4 Valve

Claims (5)

An iron-based sintered alloy valve seat in which hard particles and solid lubricant particles are dispersed in a matrix phase,
The matrix phase is a fine carbide precipitation phase in which fine carbides having a particle size of 10 μm or less are precipitated and having a Vickers hardness of 550 HV or more,
The hard particles have a Vickers hardness of 650 to 1200 HV,
In the matrix phase, the hard particles are dispersed in an area ratio of 20 to 40%, and a diffusion phase is formed around the hard particles in an area ratio of 0% to 5%, and the solid lubricant particles are formed in an area ratio. A valve seat made of an iron-based sintered alloy for an internal combustion engine having excellent wear resistance, characterized by having a structure dispersed in an amount of 0 to 5%. The matrix including the matrix phase, the diffusion phase, the hard particles, and the solid lubricant particles is in mass%,
C: 0.5-2.0%, Si: 0.5-2.0%,
Mn: 5% or less, Cr: 2-15%,
Mo: 5-20%, Co: 2-30%
In addition, V: 0 to 5%, W: 0 to 10%, Ni: 0 to 5%, S: 0 to 2%, Cu: 0 to 5%, Ca: 0 to 5%, F: 0 2. The iron-based sintered alloy valve for internal combustion engines according to claim 1, wherein the valve is composed of one or more selected from ˜5%, and has a composition composed of the balance Fe and inevitable impurities. Sheet.   The hard particles contain, in mass%, Cr: 3 to 15%, Mo: 20 to 40%, Si: 0 to 3%, Fe: 0 to 3%, and the balance from Co and inevitable impurities Mo-Cr-Co intermetallic compound particles, including Mo: 20-30%, Ni: 5-20%, Cr: 15-35%, further containing Si: 0-3%, the remainder Co and unavoidable Mo-Cr-Ni-Co-based intermetallic compound particles composed of mechanical impurities, Mo: 20-40%, Cr: 3-15%, Si: 0-3%, balance Fe and inevitable impurities Mo-Cr-Fe-based intermetallic compound particles comprising Mo: 30-50%, Fe: 15% or less, further containing Cr: 2-8%, Si: 0-4%, the balance Co and The iron-based sintered alloy for internal combustion engines according to claim 1 or 2, characterized in that it is one or more selected from Mo-Fe-Co intermetallic compound particles composed of inevitable impurities. Valve seat made. 4. The internal combustion engine according to claim ₂ , wherein the solid lubricant particles are one or more selected from manganese sulfide MnS, molybdenum disulfide MoS ₂ , and calcium fluoride CaF _2. Valve seat made of iron-based sintered alloy for engines A combination of a valve and a valve seat,
The valve is a valve whose surface hardness of the contact surface with the valve seat is Vickers hardness of 400 to 1300 HV,
A combination of a valve and a valve seat excellent in wear resistance, wherein the valve seat is the valve seat made of an iron-based sintered alloy for an internal combustion engine according to any one of claims 1 to 4.

Images